docs: add Jupyter notebook tutorials for key topics

Add 6 new interactive Jupyter notebooks covering:
- phaseEnvelope.ipynb: Phase envelope calculations with plotting
- TEGdehydration.ipynb: TEG gas dehydration process
- hydrateFormation.ipynb: Gas hydrate calculations and inhibition
- gasCompression.ipynb: Single/multi-stage compression
- PVTexperiments.ipynb: CCE, DL, CVD and separator tests
- separatorDesign.ipynb: Two/three-phase separation and optimization

Based on topics from NeqSim-Colab repository.

Author: EvenSol